The microwave radio frequency (RF) spectrum is extremely congested due to the rapid growth of various RF system applications. The performance of a given RF system is degraded by radio frequency interference (RFI). Constellations of satellites, whose field of view encompasses the entire globe, are currently used to allow communication between radio devices or radio receivers throughout the world. These constellations can be either in geostationary synchronous orbits (GSO) or non-geostationary synchronous orbits (non-GSO), also called low-earth and medium-earth orbits.
Several low-earth orbit mobile satellite systems have been proposed and at least one, which uses code division multiple access (CDMA), is expected to be deployed in the 1998/99 time frame. It will provide global coverage for hand-held and mobile user terminals (UT). This system will use L-band (1610-1626 MHz) for UT-satellite links, S-band (2485-2500 MHz) for satellite-UT links, and C-band (about 5 GHz) for satellite-to-gateway and gateway-to-satellite links.
One problem with satellite communication systems is directly related to the increased use due to new RF system applications. New RF systems compete with existing systems for available bandwidth. Over the past several years, for example, mobile phone use has increased dramatically putting a heavier burden on current satellite communication systems.